In an internal combustion engine powered vehicle, the primary function of the inlet diffuser (also called a snorkel) on the engine's air cleaner is to supply air to the air cleaner with low airflow restriction and low induction noise. The inlet of the diffuser is typically small to reduce radiated induction noise and the outlet area is large to minimize air cleaner flow restriction.
Heretofore, air cleaner snorkels have been shaped like conventional straight symmetrical diffusers so as to operate to expand the high speed incoming air to the snorkel to a low exiting speed as low speed air entering the air cleaner has less restriction than high speed air. While the straight symmetrical diffuser has been found to be the most efficient shape for an air cleaner inlet, they tend to be very difficult to package in modern aerodynamic cars which because of fuel economy reasons have been downsized and streamlined resulting in a substantial reduction in the size of the engine compartment and in particular the space for the air cleaner with its snorkel. For example, it is often required that the air cleaner inlet be short and wind through a crowded engine compartment. However, for a straight diffuser to perform well it must normally exceed ten inches in straight length which is a requirement that conflicts with available modern underhood space.